1. Field of the Invention
The relief valve is installed in piping systems, pressure vessels and other applications to relieve overpressure and thus prevent damage to the system.
2. Description of Related Art
Samuel E. Gilmore, the founder of Gilmore Valve Co., invented a Relief Valve, which is the subject of U.S. Pat. No. 3,601,149, which was issued on Aug. 24, 1971. Several prototypes of this Relief Valve were produced with a single outlet, but it was too expensive to sell because of the complex design. This prior art valve, as taught in the patent, utilized a movable seal carrier, sometimes referred to as a conduit means, to transport opposing coaxial seal tubes from a closed position to an open position. These seal tubes engaged opposing coaxial cylindrical plugs. Each cylindrical plug was held in place by an outer portion of the body. One of these outer body portions contained the outlet of the valve and the opposing outer body portion was blank. In other words, the valve had a single inlet port and a single outlet port.
In the open position, the valve was designed to allow fluid to flow from the inlet through an internal bore in the body and another bore in one of the cylindrical plugs to the outlet. Apparently, this valve was never even prototyped with two opposing coaxial outlets although the patent points out that xe2x80x9cif desired, both outer portions could include outlets.xe2x80x9d In an alternative embodiment, one of the cylindrical plugs contained a bore and the opposing plug was merely blank because there was no fluid flow on the side of the valve opposite the outlet. The purpose of this second blanked port was to permit installation of the internal valve components. The Relief Valve of U.S. Pat. No. 3,601,149 was a commercial failure because of its complexity and expense and was never sold in any configuration.
After more than a decade had passed, another engineer at Gilmore Valve Co. developed a different design that was less complex and therefore more economical to produce. U.S. Pat. No. 4,456,028 for a Relief Gate Valve was issued in 1984 and was assigned to Gilmore Valve Co., the assignee of the present invention. This Relief Gate Valve is shown in cross-section as FIG. 1 of the present patent application. This prior art valve had a single inlet port and a single outlet port. The prior art valve of FIG. 1 has been produced and sold in huge commercial quantities by Gilmore Valve Co. and is a commercial success. However, there is still a need for a relief valve that has larger flow capacities at lower overpressures than the valve of FIG. 1. For more than 30 years, a double port relief valve was not available from Gilmore Valve Co.
Relief valves are placed in piping systems, pressure vessels and other systems to vent excess pressure from the system to prevent damage to the system, to the environment and to individuals. It is essential that the relief capacity of the valve meet or exceed the maximum potential capacity of the system to prevent excessive pressure and possible explosion. Traditionally, there were two standard solutions to the need for greater flow capacity. The first solution was to put two or more valves in parallel which more than doubles the cost of the system and makes it more complex to install and maintain. The other traditional alternative was to install a bigger valve with a bigger spring, a bigger outlet and bigger piping. Both of these traditional solutions are expensive. There is therefore a need for a more economical solution to the problem of increased flow through relief valves.
There is a need to keep overpressure in relief valves and systems to a minimum. Overpressure is the amount of pressure build up in a system over the set pressure of the relief valve to achieve the required relief capacity. For example, if the set pressure of a relief valve is 5,000 psi, it will begin to open at 5,000 psi. However, the pressure in the system and the relief valve may continue to rise because most liquid relief valves typically do not snap to the full flow open position at the set pressure (sometimes referred to as set point). Instead, relief valves typically open only a little at set pressure, and higher pressure will open the valve even further. For example, some relief valves might not achieve a full open position until the pressure in the system is 6,000 psi. In this example, the valve experienced 1,000 psi of overpressure. When a relief valve is open and flowing, the flow rate is also sometimes referred to as relief rate. Excessive overpressure is undesirable because it places a strain on piping and vessels and can result in catastrophic failure/explosion.
After relieving, the system pressure must drop below the set pressure before the relief valve will re-seal. The pressure where this occurs is called the reset pressure and the pressure band between the set pressure and reset pressure is referred to as the blowdown dead band. Blowdown dead band is primarily a function of seal friction. Blowdown dead band is typically expressed as a percentage of the set point. For example, if the set point is 5,000 psi, and the blowdown dead band is 20%, system pressure must fall to approximately 4,000 psi before the relief valve will close and reseat. High blowdown dead bands in this type of relief valve are undesirable. There is a need to reduce the blowdown dead band in relief valves with increased flow rates.
The double port relief valve of the present invention doubles the relief rate for a given overpressure when compared with the prior art single port valve (i.e. FIG. 1). In an alternative embodiment, the dual port stacked spring relief valve (FIGS. 16 and 17) quadruples the relief rate for a given overpressure when compared with single port prior art valve (i.e. FIG. 1). Improved seal designs in the present invention reduce the friction when compared with prior art designs. The single port prior art relief valve (i.e. FIG. 1) can be retrofitted to a dual port design and can then be reinstalled in the field. Retrofitting is accomplished by boring another hole in the body to create a second outlet port. A new seal assembly and seal carrier is then installed. This retrofit is a novel solution to situations that require increased flow. Use of common springs in the present invention and the alternative embodiments reduces the number of parts that must be carried in inventory to produce this line of relief valves.